To know everything about a particular subject: from the composition of the family unit to a series of other information that will allow you to have a precise picture of the individual under examination.
Before introducing people who do not know each other in familiar environments (from domestic workers to gardeners, from baby sitters to drivers, carers, etc.) it is advisable to know as much as possible about these people, who will then go to support our children and our loved ones.
Before buying and selling a property or an activity, it is advisable to know as much as possible about the property to be purchased or the real availability of the buyer.